1. Field of the Invention
The present invention relates generally to a method for detecting the level of printing material in a printer, and more particularly to accurately detecting the status of toner in a laser printer by a more efficient use of a photosensor.
2. Description of the Prior Art
In general, exemplars of the contemporary practice of printers are frequently concerned with detecting the current level of printing material that is left in the printer. In particular, laser printers are provided with toner sensing apparatus for detecting the status of toner powder in those printers. Among exemplars of the contemporary practice, Tachihara et al. (U.S. Pat. No. 5,617,121, Ink Jet Recording With Ink Detection, Apr. 1, 1997) discusses a recording head that includes discharge ports for discharging ink. An ink detection element is provided in the liquid chamber for detecting the presence of ink. Murray et al. (U.S. Pat. No. 5,610,635, Printer Ink Cartridge With Memory Storage Capacity, Mar. 11, 1997) discusses a printer ink cartridge including a memory storage element. The memory storage element is capable of storing information regarding the amount of ink remaining in the cartridge. The memory storage element is connected to the control and driver circuit to enable information to be retrieved and stored from the memory storage element. The control and driver circuit can also include a counter for counting the number of times the heating elements on the cartridge are energized. The approximate number of times the heating elements have been energized indicates the approximate number of drops of ink that have been applied by the cartridge. Stapleton (U.S. Pat. No. 5,596,351, Ink Level Sensing On A Pen Carriage In A Pen Plotter, Jan. 21, 1997) discusses an apparatus for sensing whether a liquid with a turbulent surface and contained within a vessel has fallen to a level where the liquid is substantially expended. Cowger (U.S. Pat. No. 5,574,484, Level Detection For Ink Cartridges Of Ink-Jet Printers, Nov. 12, 1996) discusses a sensor that detects the level of ink present in an inksupply cartridge of an ink-jet type printer. The sensor moves with the reciprocating pen carriage of the printer. Ogiri et al. (U.S. Pat. No. 5,508,786, Image Forming Apparatus, Apr. 16, 1996) discusses determining the number of copies which can be outputted corresponding to the defined capacity of the developer. Takayanagi et al. (U.S. Pat. No. 5,488,395, Liquid Jet Recording Apparatus, Jan. 30, 1996) discusses a liquid jet recording apparatus having a pair of electrodes provided to be immersed in the ink in the container. By applying a voltage between the electrodes, the remainder of the ink is detected by a change in the electric resistance between the electrodes. Gu (U.S. Pat. No. 5,485,191, Image Forming Apparatus Having Tone Correction Function, Jan. 16, 1996) discusses an image forming apparatus including an electrophotographic photosensitive member. For tone controls, a detector detects a state of the tone control image, and the controller controls the electrostatic latent image forming device on the basis of a datum from the detector and predetermined tone correcting information. Accatino et al. (U.S. Pat. No. 5,414,452, Recognition Of Ink Expiry In An Ink Jet Printing Head, May 9, 1995) discusses ink jet printers in which the print head is connected to an ink reservoir, such as can be used in teleprinter or facsimile apparatuses. A logic circuit is used to count the number of drops gradually expelled, and with any necessary correction, compares this number with the maximum number of drops equivalent to a known volume of ink contained on average in the reservoir. Expiry of the ink is indicated as in dependence upon the result of the comparison. Gatten (U.S. Pat. No. 5,068,806, Method Of Determining Useful Life Of Cartridge For An Ink Jet Printer, Nov. 26, 1991) discusses a computer program in the microcontroller of an ink jet printer-plotter that counts the ink dots fired by the carriage of the printer. El Hatem et al. (U.S. Pat. No. 4,853,718, On Chip Conductive Fluid Sensing Circuit, Aug. 1, 1989) discusses a situation in which the ink in an ink jet is sensed by a capacitor, one plate of which is coupled to the ground through the ink. From my study of these exemplars of the contemporary practice and art, I find that there is a need for an effective and improved device for accurate toner detection that does not require an overly accurate (and hence expensive) photosensor.